Soot oxidation over K-doped manganese and iron spinels — How potassium precursor nature and doping level change the catalyst activity

•Potassium precursor nature is of high importance for Fe3O4 surface promotion.•The level of doping plays a different role for iron and manganese spinel catalysts.•High level of K addition to Mn3O4 leads to most active superficial birnessite phase.

This paper describes catalytic investigations into soot oxidation over KOH, K2CO3, KNO3, CH3COOK and K2SO4 doped iron and manganese spinels. For Fe3O4 it was found that alkali doping (0.5 monolayer) is confined to the surface and results in the substantial enhancement of its catalytic activity (ΔT50% ≈ 80 °C for K2CO3), depending on the precursor nature. For Mn3O4 K-doping at low loading (0.5 ML) has a negative effect, whereas at high loading (9 ML) leads to the formation of a birnessite shell on the Mn3O4 core catalyst with a spectacular increase of the soot oxidation rate (ΔT50% ≈ 150 °C).

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